1. (Field of the Invention)
The present invention relates to a control method, a monitoring method, and a control device for a batch type or a continuous type kneader for kneading a high-molecular material (polymer).
2. (Description of the Prior Art)
In the field of kneading of polymer, a batch type closed kneader called a Banbury mixer or a continuous type mixer having a material feeding unit and a kneading unit is widely used to compound various additives into the polymer and knead a compound thus obtained. As an recent example of the continuous type mixer, a biaxial extrusion kneader additionally having an extruding unit at the end of the kneading unit is also widely used. As the condition for satisfying the physical property of a kneaded object, a uniform degree of plasticity of the kneaded object and a uniform degree of dispersion of compounding additives such as fillers and chemicals are required. To meet this requirements, it is necessary to control a charge time of the additives (charge position in the continuous type), a kneading end timing (material residence time), and other various operating conditions.
Conventionally, the control of a kneading step in the batch type or the control of the kneading unit in the continuous type is conducted by adjustment in setting of the kneader on the basis of empirically determined time, temperature, and power consumption. That is, a sample of a kneaded object is first prepared. Then, a charge quantity (feed quantity), a charge order (charge position), and operating conditions (rotor speed, cooling condition, and material filling quantity) are empirically decided from the result of preparation of the sample. As parameters for deciding a charge time (charge position) and a discharge time (residence time), the reference values of a kneading time, kneaded object temperature, and power consumption are defined, and some of these are employed as a manufacturing standard to conduct the operation of the kneading step. In actual, however, there occur variations in the degree of plasticity and the temperature of polymer, slippage of the charge time, timewise change in tip clearance between a kneading rotor flight and a chamber, and fluctuations in various machine operating conditions, such as fluctuations in machine temperature and rotational speed. Because of these factors, the degree of plasticity of the kneaded object and the degree of dispersion of the compounding additives such as fillers or chemicals are varied even though the kneading temperature and the kneading time (residence time) fall within a tolerance of the reference values. Accordingly, in the case of excessive kneading, there occur a reduction in productivity, defectiveness of physical property, energy loss, variations in quality, etc. In the case of deficient kneading, there occur defectiveness of physical property, etc. In the case where the time of charging the additives slips, there occur defectiveness of physical property, variations in quality, etc. Further, since the conventional operating conditions (rotor speed, cooling condition, and material filling quantity) are fixed from the start to the end of kneading, they disaccord with the physical property varying from bleeding to viscosity reduction, resulting in inefficient kneading.
To solve this problem, there has been conventionally proposed a kneading control method for a closed type kneader employing a control circuit storing as reference elements a power consumption reference pattern for a rotor driving motor and an operating condition reference pattern. The power consumption reference pattern is so set as to correspond to a kneading step in a proper operation of the closed type kneader. The operating condition reference pattern is so set as to predetermine a proper range of a machine temperature condition of the closed type kneader corresponding to a kneading step. In accordance with the operating condition reference pattern, various operating conditions are kept in the proper range. On the other hand, a power consumption of the rotor driving motor during operation is detected, and an actual power consumption based on a detection signal is compared with the power consumption reference pattern. When there is a difference therebetween, the operating condition relating to the power consumption is adjusted within the proper range, whereby adjusting means for various operating conditions are controlled so that the actual power consumption follows the power consumption reference pattern (Japanese Patent Publication No. 60-33530).
This control method conducts the detection of a power consumption and feedback control from viscosity reduction of the kneaded object. Accordingly, this control method is useful in a compound showing univocal correspondence between viscosity reduction and dispersion of carbon, filler, or other materials which dispersion finally decides the physical property, or quality of the kneader object. However, the above control method does not conduct direct control from the dispersion of carbon, filler, or other chemicals in connection with recent trends of various compounds and high quality to be demanded. Accordingly, in a compound not showing the univocal correspondence between the viscosity reduction and the dispersion, the viscosity is satisfied, but the dispersion deciding the final quality is not satisfied. Thus, in many cases, the final quality is not satisfied, and resultantly the above control method is unusable. Further, the dispersion of the final compound is not controlled, but a hysteresis of kneading is followed to result in accumulation of error. Accordingly, the final quality of the kneaded object becomes unsatisfactory in many cases regardless of the fact that electric energy falls within a reference range.